In certain applications, large scale structures such as buildings and ships are fabricated from steel, a traditional structural material. Similarly, a deckhouse on a ship may be fabricated in a shipyard from steel panels. In such structures, a single wall, floor, or ceiling of the building may be formed from a number of steel panels welded together. The entire structure is further welded to the steel deck of the ship.
Compared to steel, composite materials are much lighter in weight and exhibit good corrosion resistance. Composite materials are formed of reinforcing fibers within a resin matrix. Parts fabricated from composite materials can be made strong and stiff and can be used to advantage in structural applications. However, parts fabricated from composite materials are often more costly than steel parts. The higher cost is generally due to the greater cost of the raw materials coupled with greater tooling and labor costs. Also, composite elements are more complex to join than steel plate and frame structures, which are typically joined relatively simply by welding. Thus, the composite materials may not be used to replace steel, even if their benefits would be advantageous in a particular application, due to cost considerations.
The vacuum assisted resin transfer method (VARTM) is a batch process that can be used to form composite materials into complex three-dimensional shapes. This method requires the fabrication of a mold in the final form of the part to the manufactured. The raw material is cut into appropriately sized pieces and laid up in layers in the mold. The distribution media, hoses, vacuum lines and resin lines are set. Then the resin is injected and allowed to cure. The part is then unbagged and demolded. The support materials must then be disposed of and the mold cleaned, and the entire process repeated for the next part. This process is costly due to the higher raw material costs, the hand labor required, single part processing, long cure cycle, and the amount of scrap material generated. Thus, the cost per pound of VARTM composites is high compared to steel fabrication.
Pultrusion is another known fabrication process for forming composite material parts. Pultrusion is generally more suitable for forming two-dimensional shapes. The initial tooling costs can be high, but pultrusion is a continuous process from which many parts can be formed relatively economically with less labor than VARTM. Thus, in certain applications, pultrusion can be more advantageous than VARTM.
Both VARTM and pultrusion are not yet as cost efficient as steel fabrication, however. Thus, a composite material fabrication process that is competitive with steel fabrication for large scale structures would be beneficial.